1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and to a semiconductor device, and in particular, relates to a method of manufacturing a kind of a semiconductor device which has a metal electrode structure and to such semiconductor device.
2. Description of the Related Art
Conventionally, in an attempt to achieve a high performance semiconductor device, downsizing of a MOSFET (metal oxide semiconductor field effect transistor) has been in progress. Downsizing of a MOSFET can be achieved, for example, by thinning down a silicon oxide film (SiO2 film) which is to serve as a gate insulator. When the SiO2 film is thinned down, however, gate leakage current will increase due to tunnel current. Therefore, with a post-0.1 μm generation device, there has been a limit to how far the gate insulator can be thinned. Furthermore, with such post-0.1 μm generation device, depletion occurring in the gate electrode is a serious matter which cannot be disregarded. Accordingly, it has been difficult to reduce the effective film thickness of the gate insulator.
From this perspective, in recent years, a method adopting a metal oxide such as HfSiON or the like, being a high-dielectric material, as a material for the gate insulator has been proposed. With such technique, the SiO2 conversion thickness of the gate insulator (i.e. the effective film thickness of the gate insulator) can be reduced while keeping the actual physical film thickness of the gate insulator, whereby the device can be downsized while at the same time possible increase in the gate leakage current can be prevented.
Moreover, when the physical thickness of the gate insulator is less than 1 nm, it is difficult to achieve such FET where a polysilicon is used as a material for the gate electrode as in a case of a common FET. From this perspective, conventionally, a method with which the effective film thickness of the gate insulator can be thinned down while capacity decrease due to depletion in the electrode can be prevented at the same time by using a metal as a material for the gate electrode to be formed on the gate insulator has been proposed.
However, in a case where the metal film for gate electrode formation is formed directly on the gate insulator, there is a possibility that a surface of the gate insulator could be damaged through the metal film formation process, due to which deterioration in FET performance such as reliability decline with the gate insulator, mobility decline due to occurrence of fixed charges, and so forth, could occur.